201# is to contain manganese taller, the surface is very bright those who contain dark black is bright, contain manganese to be higher rust easily. 304# contains a lot of chromium, with a matte surface and no rust. The most important thing is that the erosion resistance is different. The corrosion resistance of 201# is very poor, so the price is much cheaper.
The difference between # 201 and # 304 is the nickel problem. Moreover, the price of # 304 is relatively high now, but the price of # 304 at least can ensure that it will not rust in the use process. (stainless steel potion can be used for experiment)
Stainless steel is not easy to rust is due to the formation of rich chromium oxide on the surface of the steel body can protect the steel body,201# material belongs to the high manganese stainless steel than 304# hardness, high carbon low nickel.
In southern China, the rain is hot and humid, so 201# will rust and 304# will be practical. Winter wind area, both appropriate, in the economic premise is not very abundant can choose 201#, in the economic premise allows the case or just in case of the case is recommended to use 304#.